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Mumps Outbreaks

Mumps outbreaks can occur any time of year. A major factor contributing to outbreaks is being in a crowded environment, such as attending the same class, playing on the same sports team, or living in a dormitory with a person who has mumps. Also, certain behaviors that result in exchanging saliva, such as kissing or sharing utensils, cups, lip balm or cigarettes, might increase spread of the virus. In some years, there are more cases of mumps than usual because of outbreaks.

Mumps outbreaks can still occur in highly vaccinated U.S. communities, particularly in close-contact settings. In recent years, outbreaks have occurred in schools, colleges, and camps. However, high vaccination coverage helps limit the size, duration, and spread of mumps outbreaks. MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease. Two doses of the vaccine are 88% (range: 66 to 95%) effective at protecting against mumps; one dose is 78% (range: 49% to 92%) effective. Studies have shown that the MMR vaccine protects against currently circulating mumps strains.

Although it is not mandatory to report mumps outbreaks to CDC, many health departments will contact CDC when they experience an unusually high number of cases. In 2016 and 2017, a number of cases and outbreaks have been reported to CDC, primarily associated with college settings. These outbreaks have ranged in size from a few to several hundred cases, have mostly affected young adults, and are likely due to a combination of factors. These factors include the known effectiveness of the vaccine, waning immunity following vaccination, and the intensity of exposure to the virus in close-contact settings (such as a college campus) coupled with behaviors that increase the risk of transmission.

Mumps Trends

Before the U.S. mumps vaccination program started in 1967, about 186,000 cases were reported each year, but the actual number of cases was likely much higher due to underreporting. Since the pre-vaccine era, there has been a more than 99% decrease in mumps cases in the United States. Since the two-dose vaccination program was introduced in 1989, mumps cases have ranged year to year from a couple of hundred to several thousand. However, in recent years, there has been an increase in the number of reported cases, from 229 cases in 2012 to 6,366 cases in 2016. The recent increase has been mainly due to multiple mumps outbreaks reported across the country in settings where people often have close contact with one another, like college campuses.

Past Mumps Outbreaks

In 2016-17, a large outbreak in a close-knit community in northwest Arkansas, resulted in nearly 3,000 cases.

In 2015-16*, outbreaks were reported from several university campuses, including a number of smaller outbreaks with limited spread. The two largest outbreaks were from Iowa and Illinois, each involving several hundred university students; both held wide-scale vaccination campaigns.

In 2014, several outbreaks affiliated with universities were reported from multiple states, including one community outbreak in Ohio linked to a university that involved over 400 people, and an outbreak affecting the National Hockey League.

In 2011-2013, there were several smaller mumps outbreaks reported on college campuses in California, Virginia, and Maryland. However, these all had limited spread, and national case counts for these years were at several hundred cases per year.

In 2009 to 2010, two large outbreaks occurred.

One multi-year outbreak involved over 3,000 people and mostly affected high school-aged students who were part of a close-knit religious community in New York City and attended schools in which they had very close contact. The outbreak started when an infected student in this religious community returned from the United Kingdom where a large mumps outbreak was occurring.

The second outbreak involved about 500 people, mostly school-aged children, in the U.S. Territory of Guam.

In 2006, the United States experienced a multi-state mumps outbreak involving more than 6,500 reported cases. This resurgence predominantly affected college-aged students living in the Midwest, with outbreaks occurring on many different Midwestern college campuses.